Hypertrophic cardiomyopathy (HCM), a disease characterized by abnormal thickening of the ventricular myocardium, is a common genetic cause of heart failure and sudden death. The prevalence of this condition is 1:500, and over the last twenty years there has been tremendous advancement in understanding the genetic underpinnings of this Mendelian disorder. However, despite the robust genetic knowledge that exists for this disease, the development of novel treatments has been limited. The genes implicated in HCM encode for cardiomyocyte sarcomeric proteins, and select rodent models have been created that model components of the disease process. However, performing a large scale screen for novel therapeutics using mammalian animal models is cost and time prohibitive. Recently, the emergence of the larval zebrafish as a tool for disease modeling and phenotype-driven small molecule screens has provided a viable alternative to mammalian model systems. We recently developed a zebrafish model of a human hypertrophic cardiomyopathy mutation in cardiac Troponin T. A comparison between our zebrafish model and a mouse model of HCM, discovered that the cardiac natriuretic peptide genes, nppa and nppb, were robustly induced in both HCM models. Utilizing this discovery, we created a zebrafish transgenic reporter line that models the pathologic activation of the nppb gene. We then performed a targeted kinase inhibitor screen to identify pathways important in the pathological induction of nppb secondary to hypertrophic stimuli. We discovered that mitogen-activated protein kinase kinase (MEK1/2) was important in the pathological induction of this signaling pathway. This application is focused on investigating the role of the Raf/MEK signaling cascade in the pathophysiology of sarcomeric gene mutations. Aim 1. Determine which components of the Raf-MEK signaling cascade are important in HCM pathophysiology. Utilizing a zebrafish model of a sarcomeric gene mutation, we will test which components of the Raf-MEK signaling cascade are important in activating hypertrophic signaling pathways in vivo. We will target these pathways using a combination of small molecule inhibitors, and genetic knock down techniques. Aim 2. Delineate the effect of selective inhibition of MEK signaling in a mammalian model of HCM. We will determine if pharmacological inhibition of MEK signaling can prevent the development of disease in a mammalian model of hypertrophic cardiomyopathy. Frist, we will determine the developmental timing of when sarcomeric gene mutations initiate the hypertrophic signaling cascade so that we can define a prehypertrophic and hypertrophic interval. We will then selectively target MEK1/2 using a small molecule inhibitor to determine if targeting this kinase can prevent the development of HCM without causing cardiotoxicity. Hypertrophic cardiomyopathy caused by sarcomeric gene mutations is a common inherited cardiovascular condition with no effective methods to prevent the development of disease. We will utilize novel in vivo models to determine if manipulation of the Raf-MEK signaling pathway is an effective method to prevent the development of ventricular hypertrophy caused by sarcomeric gene mutations.